1. Field of the Invention
The present invention relates to a steering shaft locking device which locks a steering shaft upon the removal of a key from a key rotor which has been turned to the locking position with the key.
2. Discussion of the Related Art
In a typical steering shaft locking device, when a key is removed from a key rotor which has been turned to the locking position (LOCK position) with the key, a locking member is moved by the elastic force of a spring to a lock position to engage a groove formed in a collar fixedly mounted on a steering shaft, thereby locking the steering shaft and preventing its rotation. When the key is inserted into or extracted from the key rotor and the rotor is in the LOCK position, a key response member pivots with the insertion and extraction of the key. When the key rotor is turned to any one of the operating positions (ACC, ON and START positions) with the key, a cam member is turned together with the key rotor, so that the locking member is moved to a release position against the elastic force of the spring; that is, the locking member is disengaged from the groove formed in the collar. Thus, the steering shaft has been unlocked and may rotate. In this operation, the key response member, engages an engaging portion of the locking member, so that the locking member is held at the release position.
As was described above, the locking member is urged to the lock position by the elastic force of the spring. Such a device may be overcome undesirably to allow rotation of the steering shaft by insertion of a dummy key into the key rotor held at the LOCK position. A dummy key of this sort can fit into the key rotor, but will not allow the key rotor to turn. If the locking member is pushed toward the release position against the elastic force of the spring by some method, the locking member is moved to the release position and held there by the key response member. Thus, the steering shaft can be unlocked with only a dummy key and without turning the key rotor.
In order to eliminate the above-described difficulty, the present applicant has proposed the steering shaft locking device disclosed in Japanese Utility Model Application No. 21286/1986. This steering shaft locking device includes a stopper member movably coupled to the locking member, and a cam plate having a locking portion for a cam member which is turned together with the key rotor. When the key rotor is turned to the LOCK position, the cam rotates, causing the locking portion of the cam plate to abut a stopper part of the stopper member, and preventing the movement of the locking member to the release position. The locking member cannot be moved to the release position until the key rotor is turned to an operating position with the key, whereupon the locking portion of the cam plate disengages a stopper part of the stopper member.
However, the above-described steering shaft locking device has several disadvantages. For example, since the cam plate having the locking portion is separate from the cam member, a large number of components in the steering shaft locking device is required. Similarly, assembly of the locking device requires a large number of assembling steps.